This invention relates to full color organic light emitting display devices and methods of making them.
Organic light emitting devices (OLEDs) are useful for a variety of applications including displays, graphic signs, and lighting applications. High resolution OLEDs that can provide a full range of colors are particularly desirable. Commercial development of full color OLEDs requires patterning the light emitting area, i.e., the pixel, with three primary colors (red, green, and blue) to provide a full color display.
The present invention features a novel method of making an organic light emitting color display panels using vacuum angle-evaporation techniques.
In one aspect of the invention, the inventors have found that, surprisingly, if a blue dopant is deposited with a red or green dopant during the construction of a pixel, the red or green color will dominate. This is an important factor in producing a full-color light emitting display. In another aspect, the inventors have found a way to correct for parallax during the making of a display panel. This is an important factor in producing large high resolution display panels.
One aspect of the present invention provides a method of making organic light emitting pixels having red, green, and blue subpixels on a display panel comprising:
for each pixel depositing a hole transporting layer and an electron transporting layer; and depositing red, green, and blue dopants simultaneously in a host layer such that the blue dopant is deposited on the blue subpixel and at least one of the red and green subpixels. The host layer may be the hole transporting layer, the electron transporting layer, or a layer between the hole transporting and electron transporting layers.
Another aspect of the invention involves using a shadow mask during the deposition process. The shadow mask may be integrated into the display panel, or may be removable and, optionally, reusable. The integrated mask may comprise photoresist, including dry film photoresist. The removable mask may be made from crystalline material (such as silicon), metal, or polymer.
In another aspect of the invention, the red and green dopant sources may be located on opposite sides of the display at an angle of about 20xc2x0 to about 70xc2x0, typically 40xc2x0, from the pixel surfaces and the blue dopant and other material sources may be located in a plane that bisects the substrate and is normal to a straight line that connects the red and green dopant sources.
In another aspect of the invention, the deposition paths of the red and green dopants are isolated from each other and the other sources with shields that start at the red and green dopant sources and extend some distance toward the pixel surface.
Another aspect of the invention provides a method of correcting for parallax in the making of an organic light emitting display panel comprising using line-of-sight vapor deposition to create a series of adjacent pixels, each pixel comprising sub-pixels, wherein one or more sources are positioned at an angle of about 20xc2x0 to about 70xc2x0, typically about 40xc2x0, from the pixel surfaces and wherein a shadow mask is used in the deposition process, the mask having slots defined by ribs wherein the pitch of the ribs is smaller than the pitch of the pixels.
Another aspect of the invention is an article comprising an organic light emitting full color display panel wherein a blue dopant is dispersed over at least one non-blue sub-pixel.
Another aspect of the invention provides an organic light emitting color display panel comprising: a plurality of full color pixels formed on a substrate, each full color pixel comprising a red, a green, and a blue subpixel, an integrated shadow mask, that corrects for parallax, for forming the color subpixels comprising a plurality of ribs erected on the substrate, wherein the pitch of the ribs is smaller than the pitch of the pixels. The integrated mask may comprise photoresist material, including dry film photoresist.
Yet another aspect of the present invention provides a removable mask for making an organic light emitting full color display panel by angled evaporation, the mask comprising a series of ribs that define slots in which individual pixels are built. The height of the ribs of the mask may be approximately equal to the width of the pixels of the display panel. The mask may also have ribs with a pitch smaller than the pitch of the pixels on the substrate for which it will be used.
As used in this invention:
xe2x80x9cdisplay panelxe2x80x9d means a two-dimensional array of individual pixels;
xe2x80x9cparallaxxe2x80x9d or xe2x80x9cparallax errorxe2x80x9d means the difference in shadow length at different points on a substrate caused by the source being a finite distance from the substrate;
xe2x80x9cpitchxe2x80x9d means the center to center distance between two adjacent structures of the same type;
xe2x80x9cpixelxe2x80x9d means an area of an image display array that can be stimulated to emit light independently of other areas; and
xe2x80x9csub-pixelxe2x80x9d means an area of a pixel that can be addressed to emit light of a particular color in a multi-color display.
An advantage of at least one embodiment of the present invention is that red, green, and blue dopants and a host layer may be deposited simultaneously in a single process step, which can make the construction process faster.
Another advantage of at least one embodiment of the present invention is that it provides a full-color display panel having high brightness, high contrast, low manufacturing costs, and excellent visibility at all viewing angles.
Another advantage of at least one embodiment of the present invention is that the removable shadow mask may be reused. Using a removable mask may also allow for a simpler process because it does not require applying material (e.g., photoresist) on the substrate to form a mask. A removable mask also results in a substantially planar substrate (after deposition and removal of the mask), which can be easier to use in subsequent processing steps.
Another advantage of at least one embodiment of the present invention is that it provides a more efficient and reliable blue-emitting subpixel having a more desirable blue color.
Another advantage of at least one embodiment of the present invention is that it allows for parallax correction, which is especially desirable for making large display panels in a chamber of a limited size.
Advantages of at least one embodiment of the present invention that includes angle-evaporation of dopants (in comparison to having discrete emitting layers) for an OLED include that the operating voltages of each of the color subpixels are nearly equal, the OLED has good quantum efficiency, improved reliability, excellent resolution between subpixels, and good color saturation.
Other features and advantages of the invention will be apparent from the following drawings, detailed description, and claims.